Sandra Bland's mother, Geneva Reed-Veal, wants a federal court in Texas to get to the bottom of what happened to her daughter, whose traffic stop and jail cell death have become a fresh rallying cry for #BlackLivesMatters activists.

This week, Reed-Veal filed a civil-rights lawsuit against Texas and Waller County officials, accusing them of violating Bland's rights from the moment state trooper Brian Encinia stopped her car last month until she was found hanging in her jail cell a few days later.

Reed-Veal's lawsuit goes to great lengths to avoid the word suicide. The term appears only once in the 46-page document -- an oblique reference to a claim by Waller County Jail officials that Bland told them she had “previously attempted to commit suicide.” But if pending investigations confirm that Bland killed herself, Bland's mother may amend her lawsuit to allege jail officials failed in their duty to protect her daughter. And if that happens, a little-noticed ruling the Supreme Court issued in June -- with facts as grim as those presented in the Bland case -- may damage Reed-Veal's chances.

In Taylor v. Barkes, all nine justices shut down a lawsuit by family members of Christopher Barkes, a Delaware man who took his own life within a day of being arrested for violating probation. Jail officials' failure to set up safeguards to keep him from hanging himself, the court ruled, was not a violation of his civil rights.

Barkes had a history of “suicidal ideations” and had attempted suicide on several occasions. This and a fuller mental-health picture were contained in Barkes’ probation file. But the intake nurse at the Howard R. Young Correctional Institution in Wilmington, Delaware, had no access to it, and Barkes only told her about one of these attempts. There also was evidence that the nurse didn’t use the latest version of a standard suicide screening form, and that a qualified mental-health professional should have conducted the screening instead.

The night before his death, Barkes called his wife and told her he "can't live this way any more," and planned to take this life. The next morning, while still in custody, he hanged himself.

This failure to properly screen Barkes and take steps to prevent his suicide, his family charged, amounted to cruel and unusual punishment -- a violation of his Eighth Amendment rights.

But a unanimous Supreme Court disagreed. “No decision of this court establishes a right to the proper implementation of adequate suicide prevention protocols,” the court said in a short, unsigned opinion that was decided without briefing or oral arguments. “No decision of this court even discusses suicide screening or prevention protocols.”

In other words, Barkes had no right to be kept alive while in custody.

If that sounds harsh, it’s because the dirty little secret of the case is that it was less about “a troubled man with a long history of mental health and substance abuse problems,” as the court put it, and more about the controversial doctrine of qualified immunity, a legal shield the Supreme Court created decades ago to protect government officials accused of constitutional wrongdoing.

The law of qualified immunity is thorny and rife with controversy. But as characterized by the court, its purpose is as simple as it is overarching: It “protects all but the plainly incompetent or those who knowingly violate the law” from being sued. And not just any law, but “clearly established” law at the time of the violation.

Plaintiffs seldom overcome this legal bar. And here, since there was no law or “clearly established” right in 2004, when Barkes died, mandating Delaware jail officials institute methods that would protect people like him from themselves, no violation occurred. That is, everything the jail did or did not do in its dealings with Barkes was perfectly reasonable and lawful at the time.

“In short,” the Supreme Court wrote, “even if the institution’s suicide screening and prevention measures contained the shortcomings that (Barkes’ relatives) allege, no precedent on the books in November 2004 would have made clear to (jail officials) that they were overseeing a system that violated the Constitution.”

What’s troubling about this ruling -- beyond overlooking the reality that jails pose a higher suicide risk than other forms of confinement -- is that it leaves unsettled whether jail officials todayhave a constitutional duty to keep people in custody from killing themselves. By leaving the issue relegated to 2004, the justices effectively immunized jail officials in the Barkescase, but failed to say when, if ever, it will be "clearly established" that people -- including Bland and others like her -- have a right to survive in a jail cell.

That right matters: The same day Bland’s mother filed her lawsuit, the Bureau of Justice Statistics announced that suicide is the most common type of death in local jails.